2-((1′-n-hexyloxy)ethyl)-2-divinyl-pyropheophorbide-a (HPPH) is a derivative of pyropheophorbide-n-hexylether, which has been developed by the Roswell Park Cancer Institute. HPPH has strong absorption at 650 nm. In addition, it has a high singlet oxygen quantum yield. As a result, it is considered that the photosensitizer which has the highest efficiency and the brightest future of development. Its structural formula is as follows:

In the photodynamic therapy experiment carried out in 5 esophageal cancer patients, at a very low dose, HPPH has exhibited a very good photodynamic therapeutic efficacy. In addition, no photosensitive side effect of skin has been observed clinically.
The research group of Dr. Pandey who was working at the Roswell Park Cancer Institute reported a method for synthesizing HPPH (U.S. Pat. No. 5,198,460; US20040044198A1; Photochemistry and Photobiology, 1991, 53 (1), 65 to 72; Organic Process Research & Development, 2004, 8, 287 to 290). Up to date, in all of the reports about HPPH, there has been no mention of its crystalline form. However, crystalline form may significantly affect a drug's stability, solubility and bioavailability. In this regard, our research group has studied the preparation method of the crystalline form of HPPH. Moreover, we have obtained a crystalline form of HPPH.